[ADD] purchase: How to set several suppliers on a product?

https://docs.google.com/document/d/1-zdQZnfIz6_3pC5fXgK8G_KDsri-tfpLfflWAS-tIXk/edit

purchase/purchases/master/suppliers.rst

@@ -2,4 +2,117 @@
 How to set several suppliers on a product?
 ==========================================
 
-*Coming soon...*
+Keeping track of your vendors can be a real burden in day-to-day
+business life. Prices can change and you might have several suppliers
+for one product. With Odoo you have the possibility to directly link
+vendors with the corresponding product and specify prices automatically
+the first time you purchase them.
+
+We will take the following example: We need to buy ``5 t-shirts``. We found
+a **Vendor**; called ``Bob&Jerry's`` and we want to issue a request for
+quotation.
+
+Configuration 
+==============
+
+Install the purchase module
+---------------------------
+
+The first step to set your suppliers on your products is to install the
+purchase module. Go into your **App** module and install the
+**Purchase** module.
+
+.. image:: media/suppliers01.png
+    :align: center
+
+.. note::
+    By installing the purchase module, the inventory and invoicing module 
+    will be installed as well.
+
+Create a Vendor
+---------------
+
+The second step is to create a vendor. In this case we'll create the
+vendor ``Bob&Jerry's``. Enter the purchase module, select 
+:menuselection:`Purchase --> Vendors` and create a new vendor.
+
+You can choose if the contact is a company or a person, fill in basic
+information such as address, phone, email,...
+
+If you did not create the contact from the purchase module you will need
+to go in the **Sales and Purchases** tab as well and indicate that the
+contact is a **Vendor** (see picture below). If the contact is created from
+the purchase module this box will be ticked automatically.
+
+.. image:: media/suppliers02.png
+    :align: center
+
+Create a product
+----------------
+
+Next we can create the product we want to buy. We don't know the price
+of the t-shirt yet because we still need to issue our **Request for
+Quotation**.
+
+To create a product enter your purchase module select 
+:menuselection:`Purchase --> Products` and create a new product.
+
+We will call our product ``T-shirt`` and specify that the product can be
+sold and purchased.
+
+.. image:: media/suppliers03.png
+    :align: center
+
+Add Vendors to the product
+--------------------------
+
+The next action is to add vendors to the product. There are two ways to
+handle this. If you issue a purchase order for the first time Odoo will
+automatically link the vendor and its price to the product. You can also
+add vendors manually
+
+By issuing a first Purchase Order to new vendor
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+When issuing a purchase order for the first time to a vendor, he will
+automatically be linked to the product by Odoo. For our example let's
+say that we issue a first purchase order to ``Bob&Jerry's`` for ``5 t-shirts`` 
+at ``12.35 euros / piece``.
+
+First create your purchase order with the correct product and 
+supplier (see picture below, or the documentation page 
+:doc:`../rfq/create` for more information)
+
+.. image:: media/suppliers04.png
+    :align: center
+
+When we save and validate the purchase order the vendor will
+automatically be added to the product's vendors list. To check this
+enter the purchase module, select :menuselection:`Purchase --> Products` and 
+select our T-shirt product. By opening the **Inventory** tab we notice that our
+vendor and its price has automatically been added.
+
+.. image:: media/suppliers05.png
+    :align: center
+
+Note that every first time the product is purchased from a new
+vendor, Odoo will automatically link the contact and price with the
+product.
+
+By adding manually
+~~~~~~~~~~~~~~~~~~
+
+We can of course also add vendors and vendors information manually. On
+the same page than previously, simply click on **Edit** and click the **Add
+an item** button.
+
+.. image:: media/suppliers06.png
+    :align: center
+
+When adding a new **Vendor** you are also able to add extra information such
+as the vendor product name or code, the validity of the price and the eventual
+minimum quantity required. These informations can be added and modified
+for existing vendors by simply clicking on the vendors line.
+
+.. image:: media/suppliers07.png
+    :align: center